A driveline of a hybrid vehicle may include an internal combustion engine, an electric motor, and a transmission to propel the vehicle. The driveline may selectively couple the engine and the electric motor to provide torque to vehicle wheels. The driveline may uncouple the engine and the motor while a driver is demanding a low driver demand torque. By uncoupling the engine and the motor, the engine may be stopped to conserve fuel and the vehicle's kinetic energy while the driveline continues to rotate and provide a lower driver demand torque. The driveline disconnect clutch may be closed to restart the engine after the engine is stopped in response to an increase in driver demand torque or other conditions. If the driveline disconnect clutch transfers more or less torque than is desired from the motor to the engine, the engine may take longer than is desired to start or a driveline torque disturbance may be observed by the driver. Therefore, it would be desirable to provide a way of operating a driveline disconnect clutch so that actual driveline disconnect clutch torque capacity is close to desired driveline disconnect clutch torque capacity.
The inventors herein have recognized the above-mentioned issues and have developed a driveline operating method, comprising: receiving inputs to a controller; operating a driveline disconnect clutch via the controller in response to a clutch stroke pressure, the clutch stroke pressure based on extending a disconnect clutch gain line from a non-zero driveline disconnect clutch torque capacity to zero driveline disconnect clutch torque capacity.
By estimating driveline disconnect clutch stroke pressure based on extending a disconnect clutch gain line from a non-zero driveline disconnect clutch torque capacity to zero driveline disconnect clutch torque capacity, it may be possible to provide the technical result of improved driveline disconnect clutch control. The disconnect clutch gain line when extended to zero driveline disconnect clutch torque capacity, may improve determination of a driveline disconnect clutch application pressure where coulomb friction is overcome and torque transfer to the stopped engine begins. The driveline disconnect clutch application pressure where coulomb friction is overcome may be referred to as the driveline disconnect clutch stroke pressure or clutch stroke pressure. Knowledge of the driveline disconnect clutch application pressure allows a precise amount of application pressure to be supplied to the driveline disconnect clutch without transferring torque to the engine so that the clutch may be prepositioned to respond to a request to start the engine. Further, by providing a good estimate of driveline disconnect clutch stroke pressure, it may be possible to more accurately determine the driveline disconnect clutch's torque transfer capacity (e.g., the maximum amount of torque the driveline disconnect clutch may transfer at the present driveline disconnect clutch application pressure) because it is known where driveline disconnect clutch application pressure in excess of the driveline disconnect clutch stroke pressure increases driveline disconnect clutch torque transfer capacity, at least until a maximum pressure is provided.
The present description may provide several advantages. For example, the approach may provide improved vehicle energy efficiency. Further, the approach may reduce driveline torque disturbances. Additionally, the approach may provide for more predictable engine starting.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.